Process for preparing moulding sand

ABSTRACT

A PROCESS IS DESCRIBED FOR PREPARING A MOULDING SAND HAVING IMPROVED PROPERTIES OVER ORDINARY MOULDING SAND AS FOR FLUIDITY, MOISTURE CONTENT, COHESION AND SCABBING RESISTANCE BY ADDING TO ORDINARY MOULDING SAND A MAXIMUM OF 2% BY WEIGHT OF PULVERIZED COCOA BEANS OR PARTS OF THEM SUCH AS GROUND COCOA SHELLS OR COCOA EXPELLERS.

May 30, 1972 Filed March 29', 1971 HT VAN DEN BERG ETAL 3,666,504

PROCESS FOR PREPARING MOULDING SAND 3 Sh8etsSheet 1 FLUIDITYA 2.2 2.4 2.6 2.8 3.0 3.2 0F MOISTURE f;

INVEN R HENDRIKVAN hzlfiRG BQERMAN s. LE mk ATTORNEYS May 30, 1972 Filed March 29, 1971 ANGLE or TILTING C- mm.

H. VAN DEN BERG FFAL PROCESS FOR PREPARING MOULDING SAND 5 Sheets-Sheet 2 I l l l I I I %OFMOISTURE B INVENTQRS HENDRIK VAND N BERG HERMAN G. LEVE LINK BY /WLA/Z Za ATTORNEYS May 30, 1972 Filed March 29, 1971 MOLDABILITY H. VAN DEN BERG ETAL 3,666,504

PROCESS FOR PREPARING MOULDING SAND 3 Sheets-Sheet 5 FIG.3

INVENTORS HENDRIK VANDEN BERG HERMAN G. LEVELINK ATTORNEYS United States P3 3 Claims priority, application Netherlands, Oct. 22, 1968,

Int. Cl. 1328b 7/34 U.S. Cl. 106-:3835 Claims ABSTRACT OF THE DISCLOSURE' A process is described for preparing a moulding sand having improved properties over ordinary moulding sand as for fluidity, moisturecontent, cohesion and scabbing resistance by adding to ordinary moulding sand a maximum of 2% by weight of pulverized cocoa beans or parts of them such as ground cocoa shells or cocoa expellers.

PRIOR APPLICATION This application is a continuation-in-part application of copending, commonly assigned US. patent application Ser. No. 867,612 filed Oct. 20, 1969, now abandoned.

STATE OF THE ART The invention relates to a process for preparing moulding sand.

The material for moulds used in the casting process mainly comprises sand with a binding agent. As a binding agent hereby as a rule clay is used. Such a type of sand is found in nature as a ready product or can be synthetically composed of quartz sand with a bentonite or another clay as binding agent.

Dependent on the nature of the castings the metal is cast into a wet or dried mould.

' For iron castings some percents of powdered coal or pitch are added to the sand for wet moulds, to. prevent that the moulding sand will adhere too strongly to the casting, while dried moulds for this purpose as a rule are provided with a coating.

The moulding sand must meet certain requirements connected with transport and storage and with the behaviour of this sand in the casting moulding proper.

In the moulding process a homogeneous ramming of the sand around the pattern must be obtained with a possibility of a good separation of mould and pattern and a casting product must be created which is free from surface defects and is an accurate copy of the pattern.

The extent to which a homogeneous ramming of the upon the fluidity of the sand.

In case of insuflicient fluidity of the moulding sand, in the mould alongside the walls of the pattern, less compacted spots are created which cause a casting with a rough surface. b

The less compacted spots alongside the wall of the moulding box and in the corners of the moulding-box may give rise to mould-wall movements during or immediately after casting causing dimensional inaccuracy of the casting.

moulding sand .can be achieved is strongly dependent The fluidity of the sand is in fact determined by the tendency towards inter-grain cohesion of the sand.

' As the tendency towards cohesion in the sand increases, already in filling the moulding-box, for instance, from a hopper this sand will show more coherence and even in this loose bulk condition less sand will reach the deeper lying and with difliculty accessible parts of the mould as a iesult of blocking.

Even the subsequent compacting operations oient to eliminate this inhomogeneity. 1

So the fluidity of the moulding sand in loose bulk condition is an important property with respect to the workability of the sand and decisive for the final condition of thecompacted mould.

Besides, the cohesion of the moulding sand in compacted condition is of importance. 7

It must be feasible to separate the mould from the pattern without mould pieces being broken off and remaining on the pattern.

This is particularly important with moulds that are lifted from the pattern by a tilting movement, which occurs fairly often in practice. The then permissable deformation of the sand can be measured by determining the so-called angle of tilting with the aid of a standard test piece. The angle of tilting thereby is the angle at which the moulding sand starts to crack.

The usefulness of clay-bonded moulding sand with respect to filling, compacting and stripping of the mould further is strongly dependent on the moisture content. This moisture content may only vary Within specific limits which limits may for instance be determined with the aid of the so-called Dietert mouldability-tester. Herewith a certain amount of sand is rotated in a drum-shaped screen for a certain time and at a certain speed. A certain percentage of the sand goes through the screen, depending on the moisture content and consequently on the tendency towards cohesion. This percentage is a measure for the mouldability of this sand, and as a rule moulding sand with a good'workability has a mouldability from to 90.

By casting metal into the mould, stresses may arise in the surface layer of the mould by a sudden heating of the moulding sand and attendant expansion. These are insufiistresses may be so great that this layer gets loose from the substrate and peeling occurs.

' A peel thus formed may bend, break off, or be eroded causing various types of scab to be created in the surface of the casting.

The tendency of the moulding sand towards this peeling, the so-called scabbing tendency, may also be determined experimentally by exposing a test piece to shockheating.

In order to be able to meet in the foundry technique the demands that are becoming increasingly higher with respect to the above properties, it is known in the art to use certain additives for the moulding sand that have an advantageous effect on these properties.

It has been found that, for instance, cellulose products, such as wood flour, powdered flax seed-vessel, powdered wheat seed-vessel and the like reduce the scabbing tendency of clay-bonded moulding sand. The influence on the fluidity, however, is very slight and negative on the angle of tilting. i

Besides, starch derivatives such as cereals, dextrin and the like in case of this sand have an advantageous influence on the scabbing resistance and stripping prop- WOI'SED.

' and but the fiuidity th en st THE INVENTION Surprisingly it has been found that a type of moulding sand can be prepared whereby the above disadvantages do not occur and whereby a' moulding sand is obtained whose. propertiesmentioned above meets the requirements without disadvantageous side-effects. arising. I

V Eorhis purpose, according to theinvention the process for preparing moulding sand fromsand, one or more binding agents and. other additives is characterized by the addition of between 0.05 to 2% by weight of cocoa beans powder. a i I By cocoa beans powder is meant a free flowingfpul- ,verized product from cocoa beans from which the greater partof cocoa butter has been removed.

. Such products showyarying. fat contents of at most by weight-An example of suchpowder products is the pulverized cocoa presscake. u

However, since this product is used as cocoa powderin beverages, it is rather expensive for technical uses.

The defatted pulverized cocoa waste products which more advantageously can beapplied in our invention are for-instance; (a) theground cocoa expeller cake (having an average fat content of 11% by weight); (b) the. ground defatted or extracted cocoa expeller cake which is also called cocoa extracted meal powder; (c) the same product after the theobromine recovery process; and (d) the ground commercial cocoa shells (having an average fat content of about 3% by weight). Kirk-Othmer Encylopedia of Chemical Technology, vol. 2, first edition, p, 890 Y and 891 illustrates how some of these products may be obtained, namely cocoa expeller cake and cocoa press cake. According to the invention the cocoa beans powder may also be added to a moulding sand that is largely compose'd of return sand, but then added in very small quantities, partly because the return sand may already. contain cocoa-beans powder from a previous moulding sand prep: aration, partly because thisreturn sand, to obtain one and the same advantageous eifect, needs a slight addition, owing tonthe condition in which the. binding agent of sandis. To moulding sand composedof new sand with a binding agent, in the process according to the invention' pre ferably 0:1-1 by weight of ground extracted cocoa expeller cake is added. v v a The, advantageous effects of the process forpreparing moulding sand of the invention are further. elucidated below with reference to some graphs and further hereinafter some examples are given of moulding-sandcompositions with which these advantageous fi'ects la re obtained. 1

As additive to the moulding sand, groundextracted cocoa-expeller cake is used. I T V In FIG. 1 the fluidity ofthe moulding sand in percentages as an ordinate at A is plotted against the moisture content in percentages as an abcis a t B.

In this FIG. 1, curve I shows the moulding .sand composed of' quartz sand, 6% by weight of sodium bentonite and 4% by weight of powder coal, with an additional? byweight of ground extracted cocoa expeller cake.

Curve 1' shows this moulding sand with the same percentages of bentonite andpowder coal,jbut' in this case with an addition of /2% by weight. of corn co bs powder and curve II shows the moulding sandwithoutaddition.

In this comparative chartcurve .I clearlyshows the improvement in fluidity of the moulding sand withthe addition of ground extracted cocoa expell'er cakeas compared with the addition of corncobs powde'r (curve I In FIG. 2 the angle of tilting as ordinate atC plotted against themoisture content as an abcis at B.

I Here curve IH the moulding sand with addition-052%"byweight of ground extracted-cocoa expeller cake, and curve III gives as an addition the same percentage by weight of corncobs powder.

In this figure curve III gives a strong improvement of the angle of tilting as compared with the moulding sand without addition (see curve IV), and further from curve III the negative influence of an addition of corncobs powder clearly emerges, this curve being even worse than the moulding sand without addition (curve IV).

Further in FIG. 3 the course of the moldability at D is indicated in dependence upon the moisture percentage at ,jFrom this figure it also appears clearly that the moulding SandT-wiIh2thQ.addItiOI1 of /2' by weight of ground extracted cocoa expeller cake (see curve V) is workable over a much wider; moisture range than. moulding sand without .such an addition or with an equal addition of corncobs powder.

When castinginto' moulding sand .withan addition of ground extracted cocoa expelle'r cake it was further found that, this addition reduces the scabbing tendency to at least the same extent as when a good quality of cereals would be used. f

Casting experiments have shown that by the improvement of the above properties of moulding sand by adding cocoa bean powder a more dimensionally accurate casting will be obtained. o By this addition the tendency towards inter-grain cohesion of the sand grains in the loose bulk condition and enveloped by clay is considerably lower. Thereby the transport of the moulding sand from the sand preparation plant to the sand hoppers can run more easily.

The tflOW of the sand from the hopper into the moulding-box will also present fewer problems, since the sand has less tendency to hang.

It is remarkable that the ground extracted cocoa expeller cake, also after extraction of, for instance, theobromine" from it,"asis applied in the chemical industry still has the same advantageous effect when added to moulding sand as" untreated extracted cocoa expeller cake.

,Examples uof compositions from which clay-bonded moulding sand according to the invention has been prepared, are: a 1V V EXAMPLE I.NEW SAND j lflflfparts' by weight of quartz sand, 6% of bentonite, 3% of powdered coal, /2% of ground extracted cocoa expeller cake'and water.

EXAMPLE H.IFACING SAND EXAMPLE. III. jUN1"r SAND 97 parts by" weight of return moulding sand, 3 parts by weight of quartz sand, 0.3% of bentonite, 0.15% "of powdered coal,'0.05.% of ground extracted cocoa'expeller cake and water. (-Note: all percentages are by Weight.) 7 In Examples No. II and III, by arepeated use of return sand, only a very small addition of ground extracted cocoa expelle'r cake is" required to maintain the" advantageous properties of the moulding sand;

Various modifications of the process and compositions of the invention may be made without departing from the spirit or scopethe'reof and it should be understood that the invention is to be limited only as definedin the appended claims. i 7

We claim:

" 1. In the processfor preparing a sand composition for foundry molds comprising mixing said with a clay binder, the improvement comprising adding to said composition 0.05 to'2.0% by weight of cocoa bean powder.

2. The process of claim 1 wherein the sand is new sand and the cocoa bean powder is ground extracted cocoa expeller cake.

3. The process of claim 2 wherein the said expeller cake is present in an amount of 0.1 to 1% by weight.

4. In a foundry moulding composition comprising sand and clay, the improvement comprising maintaining in said composition 0.05 to 2% by weight of cocoa bean powder.

5. A moulding composition of claim 4 wherein the said powder is 0.1 to 1.0% by weight of ground extracted cocoa expeller cake.

No references cited LORENZO B. HAYES, Primary Examiner US. Cl. X.R. 106-385, 38.9, 68 

